Apparently, I am not the only one who thinks it's points farming, I have seen users all over stack exchange complaining about it
The only people I've ever seen complain about this particular behavior are people who have not yet seen Jeff Atwood's blog post on the subject, which you've linked to in your question already. I understand you've only seen it very recently and it can be difficult to fully grok at first. I'll help you understand by addressing your question:
If i could use SE itself as a blog, why using a blog?
You can use SE to provide a subset of blog functionality. You can't use a question-answer pair on SE to pontificate about whether you think Vim is better than Emacs or compare Linux distributions: those are off-topic, because they are opinion-based and don't a solve a specific problem in a definitive way. You can use SE to "blog" about how you discovered and solved a tricky situation in Python, especially if you think that lots of other newbie programmers will stumble over the same problem.
Fundamentally, you need to evaluate whether the question is a good question and whether the answer is a good answer. If it helps, imagine how you'd view the Q&A if each part was written by a different person. Is the question on-topic, clearly defined, and likely to be useful to others? Does the answer actually solve the problem in a way that could be understood and used by others in the future? If so, that's wonderful; such a question and/or answer should be upvoted.
When you're a participant playing the "question-answering game" of Stack Overflow, it's easy to feel like this behavior is a kind of "cheating". You must remember, however, that the end goal of SE sites is to provide Q&A information with lasting value. If a question does that -- regardless of who asks and who answers -- then it is welcome and encouraged.
Is there anything as points farming? If yes, how to define it?
I would define "points farming" as any mechanism by which a user gains reputation without earning it by increasing the quality of the site's useful content. For example:
reputation rings or sock puppets that upvote one another's answers are a kind of "farming", because they generate reputation grossly disproportionate to (or in total absence of) whatever value they add to the site
bad-faith copying of someone else's answer in hopes of getting upvotes is a kind of "farming", because this behavior adds nothing to the content of the site (it merely repeats information already present)
Adding good content to the site is how you are supposed to get upvotes. If you can contribute that content in an on-topic Q&A format without relying on others to answer you question, that's not a problem.